In the fabrication processes for semiconductor devices, a semi-conducting wafer is normally processed through many different fabrication steps, i.e., sometimes as many as several hundred. These processing steps may include deposition processes, etching processes, ion implantation processes and a variety of other processes. The fabrication equipment utilized in these processes may include process chambers that are arranged in a cluster formation with a central loadlock chamber for delivering and withdrawing wafers to and from each process chamber.
One of the key components in a loadlock chamber is a wafer blade which is normally controlled by a robotic arm. The wafer blade is also called a robot blade by some equipment manufacturers. The robot blade can be constructed of a thin piece of metal such that it holds a wafer securely for delivering it into process chambers through narrow slit valves provided in the sides of the process chambers that join the loadlock chamber.
In a typical loadlock chamber, a robot blade and a storage elevator are provided. The loadlock chamber provides a wafer handling center in a clustered processing machine by isolating the plurality of process chambers from the surrounding atmosphere through the use of slit valves between the loadlock chamber and the process chambers. A cassette indexer or a SMIF pod may provide the source of wafers for the robot blade in the loadlock chamber. The loadlock chamber is normally provided with a self-contained vacuum system that maintains the interior of the chamber particle free and at a slightly higher pressure than the process chambers during wafer transfers to and from the process chambers. The self-contained vacuum system further provides the loadlock chamber with atmospheric pressure during wafer transfers to and from a cassette indexer. In a normal arrangement, up to about four process chambers can be mounted on a loadlock chamber.
A typical wafer holder, or robot blade 10 is shown in FIG. 1. The robot blade 10 is constructed mainly of a robot arm 12, and a wafer holder 14. The wafer holder 14 has a small thickness X such that it may go through narrow slit valves for delivering or withdrawing wafers to and from a process chamber or a cassette indexer. This is shown in FIG. 2. The robot arm 12 is constructed of a robot 18 and mechanical arms 20. The wafer holder 14 is constructed of a blade portion 22, a pair of sensors 24, 26, a pair of vacuum openings 28, 30, and a printed circuit board 32 for controlling the sensors 24, 26.
FIG. 2 and FIG. 3 show a cross-sectional view of the wafer holder 14 each holding a wafer 40 in a different position. In the configuration shown in FIG. 2, a wafer 40 is carried at the tip portion 36 of the blade 22 on top of the vacuum ports 28, 30. A vacuum is suppled to vacuum ports 28, 30 through a vacuum duct 34. The sensors 24, 26 are utilized to sense the presence of a substrate, or wafer that is properly seated or positioned on the blade 22. It should be noted that, in a conventional robot blade, only two sensors are utilized for such purpose.
As shown in FIG. 2, when a wafer 40 is carried on the tip portion 36 and secured by the vacuum force exerted on the backside 42 of the wafer 40, sensors 24, 26 of a capacitive type only sense a partial presence of the wafer 40 due to the distance existed between the wafer and the sensor. For instance, when capacitive sensors are used, a voltage of approximately between about 5 V and about 6 V is detected by the printed circuit board controller 32. The wafer handling position shown in FIG. 2 is used for delivering a wafer to a cassette indexer outside the load chamber.
In other circumstances, a wafer may be carried in pocket 38 in the blade 22 formed between the tip portion 36 and the PCB controller 32. The positioning of wafer shown in FIG. 3 is used for transporting wafers into process chambers. When the wafer 40 is positioned in the pocket 38 as shown in FIG. 3, one end of the wafer covers a capacity sensor 24 such that a voltage reading of between about 7 V and about 9 V is detected by the capacitive sensor 24 and the PCB controller 32. The voltage readings are then monitored by a machine operator as an indication of whether the wafer is properly positioned on the wafer holder 14 or not. When there is no wafer present on the wafer holder 14, a lower range of voltage, i.e, between about 2 V and about 4 V is normally detected.
While the wafer holder 14 in the robot blade 10 supplies some information about the positioning of the wafer on the wafer holder, it does not give an accurate indication of whether the wafer is properly seated on the holder. For instance, neither the position shown in FIG. 2 nor the position shown in FIG. 3 provides an accurate reading of a capacitive sensor to indicate the exact location of the wafer due to the fact that there is always a gap or distance between the wafer and the sensor. Furthermore, in the presently available robot blade system shown in FIG. 1, there is no interlocking circuit that provides a signal to interrupt a power supply to the robot blade such as to stop its motion completely when improper positioning of the wafer is detected.
It is therefore an object of the present invention to provide a wafer holder for use on a robot blade that does not have the drawbacks or the shortcomings of conventional robot blade type wafer holders.
It is another object of the present invention to provide a wafer holder on a robot blade that is equipped with a self-sensing means for detecting improperly positioned wafers on the wafer holder.
It is a further object of the present invention to provide a self-sensing wafer holder for holding and transporting a wafer in and out of a process chamber.
It is another further object of the present invention to provide a self-sensing wafer holder constructed of a holder body of generally elongated shape and at least three sensors positioned on the body to form a plane that is covered by a wafer when the wafer is carried by the holder body.
It is still another object of the present invention to provide a self-sensing wafer holder that includes a sensing circuit for determining the presence or absence of a wafer positioned on top of at least three capacitive sensors.
It is yet another object of the present invention to provide a self-sensing wafer holder which includes a sensing circuit adapted for outputting a signal to stop the motion of the wafer holder when the misplacement of a wafer positioned on top of the at least three sensors is detected.
It is still another further object of the present invention to provide a method for transporting a wafer on a self-sensing wafer holder by stopping the motion of the wafer holder when a sensing circuit receives signal from one of the at least three sensors and determines a status of misplacement of a wafer on top of the holder.
It is yet another further object of the present invention to provide a method for transporting a wafer on a self-sensing wafer holder by determining the presence or absence of a wafer positioned on top of at least three sensors by a sensing circuit.